Transistor oscillators



Jan. 2, 1962 H. F. HERBLG ErAL TRANSISTOR oscILLAToRs Filed Jan. 8, 1957 mm m mmm

United States Patent O1 Telephone and Telegraph Corporation, N utley, NJ., a

corporation of Maryland Filed Jan. 8, 1957, Ser. No. 633,066

` 16 Claims. (Cl. 179-17) This invention relates to a transistor oscillator and more particularly to an oscillator for use in a telephone sub-station to identify the subscriber on a party line.` The principal object of lthis invention is to provide yan oscillator which is inexpensive, stabile and dependable over a wide temperature .range with output in the Avoice frequency range. n

A pending .U.S. patentfapplicationby WilliamHatton for a. Party Line Identification .Syste m, Serial No: 451,791, filed August 24, 1954, now U.S. Patent No. 2,889,410, discloses a system using transistor. oscillators at party line stations. produce an oscillator for use in a telephone subset resuited-in arrangements which were 'too expensiveytoo bulky, unstable, or otherwise undependabIe.-l UsuallyA the output was transformer coupled to the line, with va separate D.C. supply path from the line. The size could be reduced, and the performance improv'edby using an oscillator without inductors, the frequency being determined by an RC circuit of a type having few components.

However, one difficulty is that characteristics vary considerably among transistors-of the same type, and with changes in temperature. Le; the D.C. collectorl current when the emitter `current le is zero, is particularly affected by such changes. The quiescent gcollector current (Ic) varies directly with Ico, causing an undesirable change in the operating point ofthe circuit. Various arrangements for establishing and stabilizing the lD.C. bias of transistor circuits have been proposed. See, 4for example, R. F. Shea, Transistor Circuits. (Wiley, 1953), chapters 6 and 8; Lo, Endres, Zawkls, Waldhaur, and Cheng, Transistor Electronics (Prentice-Hall, 1955), chapter 4; and a pending U.S. patent application by Bernard Cooper and Fred A. vMuller for a Temperature Compensated Transistor Circuit, Serial No. 552,664, filed December 12, 1955, now abandoned. A problem arises because increasing the bias stabilization reduces the gain. In some cases the operating point cannot be determined independently of the stabilization. For example, in the common emitter configuration, connecting a resistor in series with Vthe emitter terminal to provide stabilization reduces the gain considerably. The Lo et al. references discloses two bias arrangements in which a bias resistor is connected from the base to one end ofthe load resistor in the collector circuit, (l) fixed bias, with the bias resistor connected directly to the D.C. source and (2) self-bias, with the bias resistor connected directly to the collector terminal. The fixedl bias arrangement has high gain, but-the quiescent collector current Ic is unstable. The self-'bias arrangement has a large amount of feedback, both D.C. and A C., which gives a relatively stable Value for Ic, but reduces. the gain considerably.

According to the invention, an oscillator is provided using a common-emitter transistor stage with a phase- Vshifting feedback arrangement between the collector output and the emitter input. A feedback bias resistor is connected fromthe base terminal to a tap of the load resistance to provide adequate gain and stability. The operating point is determined bythe relative values of the feedback resistor and the base-tofemitter resistor. The phase-shifting arrangement preferably comprises a resistance-capacitance network.

-That and other prior-. attempts to identification arrangement; and f 3,015,696 4Patented Jan. 2, 1962 ice Accordingto a further feature of the invention, high tolerance, standard-value resistors and condensors with nominal values determined for the desired frequency `are used in thel phase-shift network, and the-frequency is trimmed to a close tolerance by using a value ,forthe feedback resistor as determined experimentally.Y y Another feature relates to the' arrangement using only two leads to connect the oscillatorin the telephone circuit, across the dial-pulsing contacts, for party identification. The load resistance is connected from the collector terminal to one lead, and the emitter terminal is connected to the other lead. When the pulsing contacts open, oscillator D.C. supply current and A.C. output current ow through the same pair yof leads. .z

In the pref/erred form of the invention, the v.required phase shift is providedby an RC network, with series connected condensersbetween the collector` andbase terminals,.and shunt connected resistorsjfrom -the respective condenser junctions and the base terminal -to the emitter terminal.` i f j According to an alternative form ofthe invention, the

oscillator is of the Wien bridge type,v with -an additional transistor input stagev having its base terminal connected by aresistor and ,capacitor in series to the output stage and by ra resistor and capacitor in shunt to ground. The abovementioned and other featuresand 'objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:

FIG. l shows a telephone system with a subscriber FIG. 2 vis a schematic diagram of an .alternateoscillator circuit.

Referringl to FIG. l, the invention is disclosed in a telephone system in which an oscillator at each station on a line transmits a tone during dialing to identify the station in a detector at arcentral office, when vmaking a toll call. A party line 15 is shown as having stations S1 to S10 with connection toa localoflice 16. Otlce 16 includes equipment for making a connection to a trunk 20 which extends to a central office 21. The connecting equipment includes a repeat coil 19 for coupling A.C. signals. The primary of -the repeat coil 19 is split and connected through respective windings vof a line relay 17 to negative and ground terminals of-acommon battery to supply D.C. current to line I15. The relay is bypassed for A.C. signals by a condenser 18.

The station S1 includes the usual telephone subset equipment of which only one set of hookswitch contacts and the dial pulsing contacts are shown. Inaddition an oscillator 11v is included, which is connected by leads 9 and 10 directly across dial pulsing contacts13. It should be noted that this connection differs from prior arrangements in that no transformer is used to couple the oscillatorvto the line 15, and only two leads are used which serve to both carry D.C. current to the oscillator and couple A.C. output to the line.

Normally when station S1 is in use, hookswitch contacts V14 being closed, the oscillator is short-circuited by contacts 13. Whenever the dial is operated, and contacts 13 open for each pulse, the D.C. current is interrupted in the usual manner to release and reoperate the relay 17. Simultaneously during each D.C. interruption oscillator |11 operates to transmit an A.C. signal, which is transmitted over line 15, through repeat coil 19 and other connecting apparatus in oflice 16, over trunk 20 to central oice 2.1. The D.C. pulses are repeated at oice 16 to trunk 20 by the contacts of relay 17 and other apparatus not shown. A connection is 1made toanother line and a station signalled accordingto the D.C.. pulses. If. a toll .call is made,- the connection may be vcompleted over a toll trunk 23 and'a'distant office 24 to the called line l25, and the station SC signalled. The calling-party identifying tone is detected by detector Vapparatus 22, which may include party identification equipment similar to that shownin the Hatton application. Each of the stations S1 to S10 includes a fsimilar oscillator, each hav= ing a separate frequency inthe voice range.

Osc'illatorfll includes a junction transistor -1'2 'vvith a phaseshift network comprising condensers C1., C2 and C3 'in series between 'the collector 'and base terminals and shunt resistors '-Rl, R2 and R3 'connected respectively from the :condenser-junction points and the transistor base terminaljtefthe emitterrerminal. Vacuumetube oseillaters using pliase#shift 'network's'if this type are disclosed 'in an a'reiIejb-y E. L. 'Ginzten and L. M. Hollingsworth, Phase- Shift seill'ators, the Proceedings 'of the LRE., vol. 29, Febary-j1941-pa`ges '43219; and in a vU.S. Patent to H. W. LNichbls, No. 1,442,781. p

A load resistance 'comprising 'resistors RLl 'and RL2 iin seriesisjeenneeted from vthe 'collecter terminal CV to lead 9, "and `th`e eritter terminal F iis connected to lead 10. Fil intel at theA junction 'ofesif's'tois R-'L`1 and -RLZ 'a fe'd ck 4resistor -RF is connected tothe base iteririiiral B. For proper vpltijn of tlie sillatr, 1i't is'` n` es'sa'y to establish a proper bias point, `to stabilize .the b is, nd 'to have suiicie'nt Tgain fr 1oscillatic'y'n. I The 'biaspon't is determined by "the rentive vaines ef 'resister RF and the resi-stance Which includes lresistf'lr -R-3 between *the ybase and 7tliie 'iemitl'te fter'ini'iia'ls. can "be shown by the metliedsfdlselesed im t-hevshe'a and inthe Le et a1. Ifeteriies 'fht'the stabilizat'ion, deirle'd as Ya aotor '-S 'Which is the Iratefeffebangeer Icwvnh las, `is apprerirrratelyffequal to The feedbaek, which reducesftheggain, depends u'pon vthe rtiof `t`o the y:total load resistance. 'It can be 'seen that adjusting the component values to improve `somegof these ctor's vi'll make 'others worse. lAccording to the invention, 'cbmponent valuesih'ave'b'een dternn'ned Willich simultaneously 'give's'atisfactory 'results lfor viall three faton With'iaSlvo'ltbattery supplying Acurrent through "17foverline11`5 tfofthi's oscillator, resistor RLZ'may tra e fa valu'ee'f zzgooojenmvsfand resister-au, 19,000 hns. Transistor l'lffis Texas 4Ir`1`str1.tinents ltype IlI2Nl85 The other cornponentfvalues depend upon frequency. V yIf hdensers C1, C2 :and C3 iareieq'ual *and resistors Rl, and R'S are equal, their theoretical values, assuming rio loading` or the phasees'hift network, are calculated'according to 7theformula d. f QWRCT/ vvl'lere `jisth'e frequency, R is the resistance of each of the resistors yR1 to R3 and C is the capacitance of each of the condensers C1 to C3. It has :been determined empirically that f'shou'ld'be approximately .0S/RC. The values used are shown in the fol-lowing table.

V It has been 'found that all these resistors may be standard 1% Watt'ivvith "5% tolerance and the V'corldens'ers nfyibe stair-dard units With 10% 'tOleralice-r The freduency-rnaybe adjusted to Within vi2%lnyjinserting a ptentioniter'in the circuitplace of resistor, 'adjusting 'thepotentiometer to 'obtain the desired -frequency,

reading the resistance value, andthen inserting a standard value resistor in place -of the potentiometer. The following standard values have been used: 0.82, 0.91, l, 1.2, 1.5, 1.8, 2.2, 2.7, and 3.3 megohms. Additional intermediate standard values can be obtained if found necessary. Prior to shipment to the eld, an additional frequency check should be made. The maximum allowable tolerance is i'4% for the finished oscillator. It has been found thate'vvith Vthe speciiied variation of resistor lRF there is suilicient output voltage, which should be noless than 0.14 volt across v600 ohms. The battery voltage at the oilice 16 may vary from 46 to l52 volts with suicient output and satisfactory operation.

This oscillator has many additional advantageous -features. The Vlarge resistor in series With the *line vvniakes variation in line f impedauce'ne'gli'gifble, and loading Aon the line Albyithe oscillatoris negligible. The relays -17vwill Y follow pulsessatisfactorily von `la line havingA a leakage resistance of A15,000 ohms or higher. The oscillator triggers and builds up oscillation rapidly. There is Yno inductive delay 'the tbuild up, since no transformer cir-other inductr 'is used.l YrIhepositive Aor negative side of the battery may be'g'rounded, by -using a PNP or NPN transistr-respectively. Here 'transistorfZ is shown as a yPNP type lWith th *positive terminal Aof the `battery grounded.

The `phase h-ift netvvo'rkf'mayfhave 'four 'or more RC sections, instead vv'of three fas] shown, to l'reduce "the gain d in tlie transistor 12, which may'fthen Abe aftype article by P. G. Slzer, "the Tapered Phase-'Shift Oscillator, Proceedings of the v31.11.12., vol. 56, `October 1948, pages 13024306, `'describes 4a method for reducing the attenuation Vin na. vphase#shift network lby tapering ythe `cimpoieit-`vlu`e`s fto lmatch the output and input impedances. The results given inthat article aref'or match. ing V4the lotvfimpedanceroutput of a vacuum tube `'to its high impedance input. It has :been 'found that @for a transistor, which has a vbigh-imp'edance output and a 'low- Iimpedance"input, the formula vshould be reversed'so that ollas (a value ero/2, oz `is C/a, Cs isc, R1 fis/e212,

-R is rzR andR-'iiskfwhere ais a constant determined according yto 'tlie'rnethods :described in the larticle. With this'arrangeinent, vvthe required gain may ybe reduced Qconsidera'bly.

"Ifhe Wien bridge loscillator 26 shown in FIG. 2 maybe connectedto Wires 9Ya11d 10 in'placeof oscillator 11 inthe systeniof'FIG. 1. Tyvo junction transistors 27 and 28, which 'maybe type 2-N44, are direct coupled. The load resistance includes Ia common resistor 229 connected ibetvveenW-ire@ and Wire V30. From`wire 30 la resistor 31 is connected to the collector terminal of the output of transistor-28, and resistor 32 is connected to the'collector of the vinput transistor-27. A resistance-capacitance net- Work comprising afconden'ser 33 'and resistor 34 in series from the collector terminal of transistor `28 lto the base terminal of transistor 27, and a condenser'BS and resistor 36 inshunt jfrom the base offtransistor A2"/ to the common Wire 10 provide regenerative feedback' and determine vthe frequency. A Vresistor 37 is connected 'from the Y'emitter lterminal -of `transistor27 to Wire 10 Which ycontrols the output Waveform. A resistor 38, vconnected from the emitter terminal of ltransistor 28 to wire 10, limits the D.C. current yan'destablishes a. good Abias point. This resistor is bypassed by Ia large condenser 39. The c'ollector terminal 'of transistor 2,7 is connected to the base terminal of transistor 28, with a resistor 40 connected to the common wire 10. Feedback resistor '741, connected from Wire 30to the base terminal of transistor 27, may have "a 'value determined experimentally tol trim the frequency'to Within a low tolerance of the desired value. D.C. bias current is'received from, and A.C. output transmitted'to, AWires 9 and 10, as for oscillator 11v in FIG. l. With'a VILlf3-volt battery at the oice 16, this oscillator produce's a 4-volt Signal across 'the 600-ohm load. This oscillator isalso easy to stabilize and control.

While we have described above the principles of ou'r invention in connection with specic apparatus, it is to be clearly understood that this description is made only by way of example and not las a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying claims.

We claim: v

l. A transistor phase shift oscillator comprising a two terminal load having a source of directl current bias and means to simultaneously connect said bias source to one of said terminals and extract oscillations yfrom said oscillator, a transistor having emitter, base and collector electrodes, Ia load resistance,` means directly connecting said load resistance between said collector electrode and said one termin-al, means to directly connect the other terminal of said load to said emitter electrode to dispose said load in a shunt relation with said transistor, a noninductive phase-shiftingmeans, means directly connecting said phaseshifting.meansbetween the collector-to-emitter output and 'base-to-emitter input of said transistor, and a feedback resistor directly connected between a given point on said load resistance andsaid b'ase electrode.v

2. A transistor phase-shift oscillator Aaccording to claim 1, wherein said load resistance comprises airst resistor connecting said collector electrode to said given `point and a second resistor connected between said given point and lsaid one of said terminals. v

3. A transistor phase-shift oscillator according toclaim l, wherein the value of said feedback resistor may be varied to vary the frequency of said output signals over a substantial range While maintaining :favorable stability, amplification, and output level.

`4. An oscillator according to claim 1, wherein said phase-shifting means comprises a resistance-capacitance 5. An oscillator for transmitting A.C. signals of a given frequency over an associated 'two-conductor line While receiving its D.C. supply power from said line, said oscillator comprising a transistor having emitter, base and collector electrodes, a phase-shifting network coupled to said electrodes including a plurality of series connected vcapaci-tors and a plurality of shunt connected resistors, one terminal of the rst of said capacitors being directly connected to said collector electrode, one terminal of the last of said capacitors and one terminal of the last of said resistors being directly connected to said base electrode, all but the l-ast of said resistors `having one terminal directly connected Ibetween successive capacitors, the remaining terminal of each of said resistors being directly `connected to said emitter electrode, rload resistance means having one terminal directly connected to said collector electrode, means for connecting one conductor of said line to the remaining terminal of said load resistance means and the other conductor of said line to said emitter electrode, and a feedback resistor directly connected between -a point on said load resistance means and said base electrode.

6, An oscillator for transmitting A.C. signals of a given frequency over an associated two-conductor line while receiving its D.C. supply power vfrom said line, said oscillator comprising a transistor having emitter, base and co1- lector electrodes, a phase-shifting network coupled to said electrodes including a plurality of series connected capacitors and a plurality of shunt connected resistors, one terminal of the rst of said capacitors being connected to said collector terminal, one terminal of the last of said capacitors and one terminal of the last of said resistors being connected to said base terminal, all but the last of said resistors having one terminal connected between successive capacitors, the remaining terminal of each of said -resistors being connected to said emitter terminal, load resistance means having one terminal connected to said collector terminal, means for connecting one conductor of said line to the remaining terminal of said load resistance means and the other conductor of said line to said emitter termi-nal, and a feedback resistor connected between a point on said load resistance n'eans andsaid base terminal, the portion ofl said load resistance between said collector electrode `and said point having a nominal value of 10,000 ohms, the portion of said vload resistance between said point and said one conductor of said line having a value of 22,000 ohms, the said plurality of capacitors comprising three capacitors of equal nominal values in the range of 0.002 to 0.04 microfarad and said plurality of shunt connected resistors comprising three resistors of equal nominal values in the range of 4,700 to. 12,000 ohms depending upon the Iassigned Ifrequency, and said feedback resistor having a value between 0.8 and 3.5 megohms.

.7. An oscillator forr transmitting A.C. signals of a givenl frequency over yan associated two-conductor line while receiving its D.C. supply power from said line, said oscillator vcomprising a transistor having emitter, base and collectorrelectrodes, a phase-shifting network coupled toV said electrodes including a plurality of series co-nnected capacitors anda plurality of .shunt connected resistors, one terminal of the first of said capacitors being connected tocsaidy collector terminal, one terminal of the l-ast of said capacitors and one terminal of the last of said resistors being connected to said base terminal, all but the last of saidv resistorsy having one terminal connected between successive capacitors, the remaining terminal of c each of said resistors being connected to said emitter ter- `niinal, load resistance means having one terminal con- 'nected to said collectorfterminal, means for connecting one conductor of said line to the remaining terminal of said load resistance means and the other conductorof said line to said emitter terminal, and a feedback resistor connected4 between Ea point on said load resistance means and said basel terminal, said transistor being a PNP juncytion type.

8. An oscillator for transmitting A.C. signals of a given frequency over an associated two-conductor line while receiving its D.C. supply power from said line, said oscil` lator comprising a transistor having emitter, base and collector electrodes, a phase-shifting network coupled to said electrodes including a plurality of series connected capacitors and a plurality of shunt connected resistors, one terminal of the first of said capacitors being connected to said `collector terminal, one terminal of the last of said capacitors and one terminal of the last of said resistors being connected to said base terminal, all but the last of said resistors having one terminalconnected between successive capacitors, the remaining terminal of each of said resistors being connected to said emitter terminal, load resist-ance means having one terminal oonnected to said collector terminal, means for connecting one conductor of said line to the remaining terminal of said load resistance means and the other conductor of said line to said emitter terminal, and a feedback resistor connected between a point on said load resistance means and said base terminal, said resistors `and capacitors having standard values with tolerances substantially higher than the desired tolerance of said given frequency, and the said feedback resistor having `a standard value determined experimentally to produce output -at a `frequency within -a low tolerance of said given frequency.

l9. An oscillator according to claim 8, wherein said resistors have a tolerance of i5%, said capacitors have a tolerance of il0%, all said capacitors and resistors except said feedback resistors have standard nominal values assigned according to the desired frequency, yand said feedback resistor has a standard value at which said oscillator has an output frequency within i2% of said assigned frequency.

l0. An oscillator according to claim 9, wherein the portion of said load resistance between said collector and said point has a nominal value of 10,000 ohms, the

portion of said load resistance between said point Iand said one conductor of said line has a nominal value of 22,000 ohms, the ysaid plurality of capacitors comprises three capacitors of equal -nomin'al values in the lrange of 0.002 to 0.04 microfarad and said lplurality of fshirit connected resistors comprises three resistors of equal nominal `values in the range of 4,700 'to 12,000 ohms depending vupon the assigned frequency, and said feedback collector electr'oizlles, a phase-shifting network coupled to 'said electrodes including av plurality of series connected capacitors and va. plurality 'of shunt connected Hresistors, one terminal of the first of said Capacitors being connected `to`sa`id collector terminal, one terminal or thev last of said capacitors 'and one terminal of the last of said resistors being eeniiecfe to 'sais base terminal, al1r but "the 1a'st of'said (resisto-rs having one "terminal connected "between suecessive capacitors, 'the remaining 'terminal or each of `said resistors being connected im said 'emitter terminal, 'load 'resistance means having one 'terminal connected to 'said collector terminal, vmeans for connecting one 'conductor of 'said line to "the remaining terminal olf said load resistance means 'and the other 'conductor of said iiiie'jfo said emitter -terminal, and 'a 'feedback 'resistor connected between 'a point'on said 'load resistance means and said baseterminal, the' capacitors and resistors of said phase- Ashifting network 'from the collector to thev base electrode -a party Vline and an oscillator operable -at a frequency assigned -for identification of said station, said oscillator comprising a transistor having emitter, base fand collector electrodes, a resistance-capacitance feedback network coupled `rbetween collector-'to-ernitter output and hase-toemitter input of "said transistor for producing oscillation at said assigned frequency, a pair lof connecting leads, load resistance means connected between 'said collector electrode and one lead df 'sain pair, sara emitter 'electrode being connected to the other lead of said pain'non-inductive means connecting said pair oli leads across said dial contacts for coupling D.C. supply power from Vsaid line 'to said oscillator 'a'nd for coupling A.C. output at Vsaid frequency from said oscillator to lsaid line only when said contacts are opened to simultaneously vtransmit a DIC. circuit interruption pulse.

` 14. vA telephone party line subscriber station Vaccording' 'to claim 13, wherein said load 'resistance means has a value of `resistance whichis substantiallyfhigher than the ieakafg'evresisfsnce of said line.

4T5. A telephone party line Vsubscriber station according `to claim '13, 'wherein said feedback network produces substantially. zero phase shift, and 'a seoond'tr'a'nsistofr coupled betweensaid 'feedback network `and the'iirst said transistor 'produces phase reversal.

16. A telephone party line subscriber station yaccording to claim '15, wherein 'said secondtransistor has emitter, base and collector electrodes, thev collector electrode of said second transistor being connected to the base electrode "of saidiirst transistor, 'the emitter electrodeof said second transistor being connected to 'the second said lead of 'said pair, and said network comprises a resistor Yand a condenserin 'series connected between the collector electrode 'of said iii-st transistor and the base electrode lof 'said Ysecond transistor Iand a resistor and a'capa-citor in shunt connected Ibetwe'e'n 'the 'said 'base electrode of said second transistor yand said second lead of said pair.

References Cited in the tile of this patent UNITED VSTATES PATENTS "Bruni i A 

